But lawyers for Susan Miller say Delta "uniformly and systematically" ignores this rule and often tells passengers they are only entitled to $25 to $50 a day in expenses.

Delta has not responded to a request for comment, but it's not the first time the company has faced this complaint: Last year, the DOT fined the airline $100,000 for failing to comply with the government rule.

Miller, a Florida resident, says she flew on Delta from Miami to Las Vegas in November of 2010.

When she arrived at her destination, Miller discovered that the airline had lost her baggage, leaving her without any warm clothes or essentials, according to a class action complaint filed in the U.S. District Court in Southern Florida earlier this month.

Miller then had to spend more than $315 to buy replacement toiletries, medication and other items, but when she raised the issue with Delta, she was told nothing could be done to help her, the court documents say. The bag turned up a couple of days later, her attorney David Tucker said.

DOT spokesman Bill Mosley declined to comment on this specific case, but said in general, carriers are not supposed to limit compensation when passengers are forced to buy essentials after their bags are delayed.

Transportation Secretary Ray LaHood has echoed this sentiment in the past.

"Travelers should not have to pay for toiletries or other necessities while they wait for baggage misplaced by airlines," LaHood said in a 2009 memo warning airlines not to improperly limit reimbursements.

A few weeks after her flight, Miller made a claim with Delta for her expenses, which was "rejected and/or ignored," her lawyers say.

"What happened to (Miller) happens every day to Delta passengers whose bags are delayed," the complaint alleges.

"Such tactics allow Delta to pocket millions and millions it would have had to pay out if it had abided by its contracts with passengers."

Miller is suing on behalf of herself and other Delta passengers who have found themselves in a similar situation.

The class action is asking for a jury trial to award direct, compensatory and punitive damages.